Hello Rajiv
I have worked with SU8 2010 and 2015 which give thickness of 10-20um. My
experience maybe slightly different than yours but I also faced similar
problems.
- For bubbles issue, I know that 2150 must be extremely viscous which
reduces the chances for bubbles to escape.
- There are a couple of ways to solve this:
1) Heat the bottle in an oven at 60C for 30 minutes and allow to
cool till room temp before spinning. Note that the bottle lid should be
half open otherwise the pressure from air inside the bottle may break it or
cause more bubbles to form.
2) Do not use a pipette for dispensing because pipette induces
more bubbles. Dispense directly from the bottle. This
greatly reduces chances of bubble formation. Also, make sure to keep the
bottle still and do not chake it much. Please open the bottle lid only when
dispensing or half open during heating....more exposure to air reduces the
solent content and makes the PR thicker and harder.
- For the issue of waviness it may be helpful to keep the wafer on a
hotplate at 30-35C and then pour directly from the bottle(to minimize
bubbles), wait for 1 or 2 seconds and then spin immediately. The
heating helps to make SU8 more flowy and hence reduces bubbles and makes
uniform layer. If there is an exhaust in your spinner then shutting it off
may help. The exhaust causes more interaction of PR with air which
evaporates solvent very quickly and causes the waviness.
- For development time you may need to increase time of exposure, and
check your UV lamp's energy. Please do a test to see how much energy the
lamp gives per minute and accordingly adjust your exposure time to match
the exposure energy mentioned in SU8 datasheet. (Sometimes the lamp's
energy reduces if regular maintenance is not done. Hence it is helpful to
test the lamp).
If you need more info then this link may help:
http://memscyclopedia.org/su8.html
On Fri, Dec 21, 2012 at 6:46 PM, Rajiv wrote:
> Dear all,
> I am using SU 8 (2150) for thickness of 800um coated on Si wafer.
> But for me problems are,
>
> (1) air bubble formation during soft baking process.
> (2)wavy surface when hight increases.
> (3) regarding SU -8 development, it takes time in hours.
> I hope there will be solution.
>
> Thanking you.
>
> Regards,
> Rajiv Panigrahi
> Research scholar
> CeNSE, IISc Bangalore
>
> Sent from my Xperia™ smartphone smartphone
>
> -------- Original Message --------
> Subject: [mems-talk] Spin-coating of thick photoresist over existing
> features
> From: João Tiago dos Santos Fernandes
> To: "mems-talk@memsnet.org"
> CC:
>
> Hi everyone,
>
> I'm currently using AZ 40XT thick photoresist to make a 20-30 µm thin film
> over a Si sample with ~30 µm high SU-8 features.
>
> The problem I am facing is the following: when I pour the AZ on top of the
> sample, tiny air-bubbles are created in areas where SU-8 features are small
> (small wells, gaps, etc) - I'm guessing that this happens because the AZ is
> very viscous and isn't able to fill those spaces and traps air. When I spin
> coat, those tiny air bubbles are spread across the sample, compromising the
> process.
>
> Is there any way to get the air bubbles out of the way without
> compromising the final film thickness? I tried low rpm for a couple of
> minutes, with no success.
>
> Thank you so much,
>
> -----------------------------
> João Tiago dos Santos Fernandes
>
> INESC Microsistemas e Nanotecnologias (INESC MN)
> Rua Alves Redol, 9
> 1000-029 Lisboa
> Portugal
>
> Tel: +351 213100237
> Email: jfernandes@inesc-mn.pt
> URL: www.inesc-mn.pt
>
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--
Best Regards
Ankita Verma
_______________________________________________
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